1. Field of the Invention
The present invention relates to a rotary electric shaver in which a rotating inner cutter with its cutter blades elastically in contact with a ring-shaped track of a substantially disc-shaped outer cutter cuts whiskers (hair) entering into the hair introduction openings formed in the outer cutter.
2. Description of the Related Art
When an electric shaver is used, vibration and noise are produced by the motor and drive system built installed in the shaver body, and, together therewith, noise (cutting noise, shaving noise, frictional noise, and the like) is produced by the vibration accompanying the friction between the outer cutter and the inner cutter and the vibration of the blades when the hair (whiskers, etc.) advanced between the outer cutter and the inner cutter is cut. In particular, the hair cutting noise and vibration noise caused by the outer cutter and the inner cutter are sensitively felt by the user because the outer cutter is in direct contact with the skin, and directly affect the quality of shaving comfort.
In reciprocating electric shavers, a plurality of arch-shaped cutter blades held in an inner cutter are caused to reciprocate and slide against the lower surface of an arch-shaped outer cutter; for such reciprocating shavers, it has been proposed, as in Japanese Patent Application Laid-Open (Kokai) No. No. 10-323461, that suitable channels be formed in the inner circumferential edges of the circular arcs of the arch-shaped cutter blades, so that the cutter blades can readily vibrate. It is also commonly known, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2005-230237 that, so as to adjust the vibration characteristics of the cutter blades, a vibration control unit comprised of, for instance, cut-ins is provided in the tip ends in the length-wise direction of the cutter blades (so as to be near the linking portions connecting the two ends of the cutter blades to the side edges thereof).
FIG. 8 shows a cutter unit used in a conventional rotary electric shaver, FIG. 9 is a side view thereof, and FIG. 10 shows the cross-section at lines 10-10 in FIG. 8.
In this conventional rotary electric shaver, the reference numeral 10 designates an outer cutter, and 12 an inner cutter. The outer cutter 10 is made of metal and is made substantially in a disc shape. The outer circumferential edge thereof is bent so as to be substantially either in a saucer-shape or inverted bowl shape.
In the upper surface of this round outer cutter 10, a multiplicity of slits 14 are formed in the radial direction. The slits 14 constitute hair introduction openings. In the upper surface of the outer cutter 10, a ring-shaped channel 16 is formed; and thus, in the lower surface (inner surface) of the outer cutter 10, two tracks 18 (only one whereof is shown in FIG. 10) comprising concentric circles are formed on both sides of the ring-shaped channel 16.
The inner cutter 12 is comprised of an inner cutter main unit 20 made of a resin and a plurality of cutter blades 22 provided on the inner cutter main unit 20. The cutter blades 22 contact the lower surface (inner surface) of the tracks 18 of the outer cutter 10 and travel while sliding on the inner surface (lower surface) of the tracks 18 when the inner cutter main unit 20 is rotated by the motor. The cutter blades 22, as shown in FIG. 10, are raised up diagonally from the attachment surface 24 which is set on, so to be attached, to the inner cutter main unit 20. More specifically, in FIG. 10, the angle a by which the cutter blades 22 are bent upward is an acute angle, and it is ordinarily 60 to 80°.
In the inner cutter main unit 20 of the inner cutter 12, as seen from FIG. 9, an engagement hole 26 is formed, and a rotary shaft (not shown), parallel to the center axis x of the inner cutter 12, is engaged with this engagement hole 26. The inner cutter 12 is rotationally driven by the rotary shaft in a direction in which the cutter blades 22 travel toward the left (in the direction of the arrow B) in FIG. 10. This rotary shaft has a tendency to return in a direction in which the inner cutter 12 is pushed against the outer cutter 10, and thus this return force is a pushing-up load for pressing the cutter blades 22 in the tracks 18 of the outer cutter 10.
In a reciprocating electric shaver, since the inner cutter moves reciprocally, the cutter blades of the inner cutter are held at right angles with respect to the direction of reciprocation motion. For this reason, it has been possible to configure the shaver so that the inner cutter itself can vibrate.
In a rotary electric shaver, on the other hand, as seen from FIGS. 8, 9, and 10, the cutter blades 22 of the inner cutter 12 are inclined so that the tip ends (cutting edge) are made to precede in the direction of travel of the cutter blades 22 (or in the direction of rotation of the inner cutter 12), thus enhancing the quality of shaving. In such a rotary electric shaver, each cutter blade 22 must have sufficient strength so as not to be bent when cutting hair, and it is also preferred that no irritating noise (buzzing sound) be produced during shaving. For these reasons, the cutter blades are made as rigid as possible to enhance the cutting quality; and more specifically, the thickness β of the cutter blade 22, in FIG. 10, is made large. As a result, since the cutter blades 22 are rigid and do not readily vibrate, it is very difficult to control the sound quality by adjusting the vibration characteristics of the cutter blades 22 by forming channels or the like in the cutter blades 22.